Klitschko, who faces Dereck Chisora on December 11, claims WBA heavyweight king Haye will go down in history as a boxing clown if he loses next month's battle of Britain with Audley Harrison.
And the WBO and IBF champion has told the Hayemaker to stop running away from a unification showdown.
The Ukrainian said: "Haye is a coward and right now he's hiding behind an excuse.
"He says will retire next year and myself and my brother Vitali must hurry up if we want to fight him.
"What is that? Either you want to fight and you face the champions or you become a clown.
"Right now, things do not look good for Haye because he is heading in the direction of becoming exactly that. He talks a lot but there is little action."
Klitschko was due to face Haye last year before the Londoner pulled out with a back injury.
The 34-year-old and his older brother Vitali, who holds the WBC title, were not convinced by Haye's withdrawal but still returned to the negotiating table with him.
Vitali believed he had agreed a bout with the Hayemaker but was left fuming when he opted to face Nikolai Valuev instead.
Haye went on to rip the WBA title from Valuev's possession and the Klitschko brothers have been chasing him ever since.
Wladimir added: "I wish the fight will happen but we proposed it twice and he bailed out twice.
"He does not have a lot of courage and is a liar. All I can say to him is, 'David, please don't get knocked out by Harrison because you will look a clown'."